1. Field of the Invention
This invention relates to a projection apparatus having an anamorphic optical system, and particularly to a projection apparatus in which an image is compressed and recorded in one direction, for example, a horizontal direction when the image is projected onto the surface of a screen. The image is used as a projected image (a projected optical element) and is laterally enlarged and widely projected onto the surface of the screen.
2. Related Background Art
A projection apparatus in which an image, compressed and recorded in a horizontal direction, is used as a projected image and which has an anamorphic optical system and a projection system (a master lens system) and in which the image is laterally enlarged and widely projected onto the surface of a screen has heretofore been proposed, for example, in Japanese Patent Publication No. 48-24048 and Japanese Patent Publication No. 62-17201.
A projection optical system of the converter type added to the master lens system will hereinafter be described with reference to FIGS. 9 and 10 of the accompanying drawings. FIG. 9 is a vertical sectional view of the projection optical system, and FIG. 10 is a horizontal sectional view of the projection optical system. The letter A designates an anamorphic lens system, the letter M denotes a master lens system, and the letter F designates a projected optical element such as liquid crystal.
The anamorphic lens system A comprises a cylindrical lens unit having negative refractive power in a horizontal direction and a cylindrical lens unit having positive refractive power in a horizontal direction, and is provided in parallel to the optical axis of the master lens system M, and the image of the projected optical element F is enlarged by the master lens system M, and is further enlarged in a horizontal direction by the anamorphic lens system A and projected.
In some cases, however, the projected image element such as liquid crystal or film is disposed while being deviated in a vertical direction relative to the optical axis of the master lens system so that the image of the image element to be projected may be projected upwardly. In the case of such a projection optical system, a large quantity of light fluxes pass through one side of the anamorphic lens system, and this tends to cause the angle at which the off-axis light flux in the vertical direction of the cylindrical lens that is incident on the anamorphic lens system to become great and cause off-axis aberrations, particularly astigmatism to increase. This state is shown in the spot diagram of FIG. 11 of the accompanying drawings. It can be well seen that as the vertical height of the image point becomes greater, the spot becomes wider and blur is created in the upper portion or the lower portion of the projected image plane.
Also, generally in a projection apparatus designed such that a projected image is disposed while being shifted in a vertical direction relative to the optical axis of a projection system and is projected in an oblique direction asymmetric to the optical system, a light ray on one side of projected light rays becomes far from a stop and becomes more separate from the optical axis. Therefore, a great distortion of the image field is created in only one side of the picture plane and this becomes an asymmetric distorted projected image.
The mounting of an additional optical system such as a wide converter onto such a projection apparatus has given rise to the problem that as shown in FIG. 40B of the accompanying drawings, the projected image 12a becomes more distorted and is difficult to observe.